The present invention relates to a method for continuously manufacturing a yarn with minimal curling tendency.
Staple fiber yarns are produced of individual fibers of a certain staple fiber length which are arranged in parallel and are bundled. These fibers are usually natural fibers, for example, wool or cotton. However, they can also be produced of synthetic fibers. For this purpose, endless filaments are cut to the required staple fiber length of natural fibers.
In order to produce a mechanically strong yarn from a bundle of staple fibers, a certain twist must be imparted to the fiber bundles that have been stretched to the desired degree of fineness. This is carried out in the spinning process which increases the fiber-to-fiber friction.
The result is a yarn with greatly improved dynamo metric properties. The greater the twist applied to the yarn under consideration of the breaking tenacity, the greater the strength of the produced yarn.
The fiber bundle, but also the individual fibers within the bundle, receives the imprinted twist (torque) only against the resistance of the inner forces of the individual fibers. Only after a certain time has passed with simultaneous release of the yarn tension, a so-called relaxation in the twisted fiber strand occurs, i.e., an equilibrium state of the inner fiber forces results, i.e., the shaping imparted by the spinning process is "frozen" or set.
When a freshly spun yarn, after completion of the spinning process, is released, i.e., is allowed to freely assume its desired orientation, the fiber bundle and the embedded individual fibers follow the so-called memory effect and will turn in the opposite direction. This results in a curled yarn. This behavior of the twisted fiber strand or fiber bundle can only be counteracted by a ripening process, i.e., a fiber-specific time period for relaxation, or by artificial fixation, for example, by a moisture/heat treatment.
For producing a twisted yarn of staple fibers, at least two spun fibers or yarns are required which are twisted about their common axis, preferably counter to the rotational direction of the spinning process. The fiber strands (spun yarns) twisted in the previous spinning process and the individual fibers within the spun yarn are subjected to a return twist which, in certain situations, can be of such magnitude that the twist generated during the spinning process is cancelled.
Due to the spinning process, the spun yarns have a shape memory that counteracts during the twisting process the imprint of the twist. Accordingly, in the twisted yarn an uneven distribution between the forces imparted by the twisting process and the forces of the return twist of the spun fibers and the individual fibers may result. This produces a twisted yarn that has a great tendency to curl whereby the magnitude of the curl tendency is a direct function of the twist of the spun yarns imparted during the spinning process, on the one hand, and the degree of twist of the twisted yarn, on the other hand.
This curling tendency of the twisted yarn can only be counteracted, as in the spun yarns, by a ripening process or artificial fixation, i.e., a moisture/heat treatment.
A multitude of different combined or integrated spinning and twisting processes have been suggested in the prior art in which directly after the spinning process the twisting process is performed.
From printed documents FR 15 52 320 and DD 78 710, dating from 1969, respectively, 1970, as well as German patent 44 31 830 and German patent 44 30 917 methods and devices are known in which with two open end spinning devices, arranged above or adjacent to one another, individual spun yarns are produced which after the spinning process are combined and subjected to a twisting process.
While the printed document DD 78 710 discloses a combined spinning and twisting process only in general terms without providing a constructive solution, German patent 44 30 917 provides a constructive solution for performing an integrated spinning and twisting process. Here, the loose individual fibers are guided into at least two open end spinning devices, positioned on a common rotor and arranged within a double twisting spindle, such that the spun yarns produced in the open end spinning devices are directly after completion of spinning twisted in the double twisting process to form a twisted yarn.
According to French printed document 15 52 320 a down twisting device (cap yarn twister) is arranged downstream of at least two stationary open end spinning rotors supported on a common machine frame. It is questionable whether, due to the different machining speeds of the open end spinning rotors, on the one hand, and the ring twisting device on the other hand this method is feasible.
According to German patent 44 30 917 the loose individual fibers are guided through the rotor axis of two open end spinning devices supported in a common rotor and the spun yarns exiting from the spinning devices are directly subjected to a single twisting process.
In order to provide a combined and continuous spinning, spooling, and twisting method, it is known to place onto a hollow spindle a yarn bobbin that has been produced in a conventional ring spindle. A roving coming, for example, from a creel, passes through a conventional stretching device and is then introduced together with the spun yarn of the yarn bobbin, placed onto the hollow spindle, into the hollow spindle axle. The yarn of the bobbin is then removed by the spindle rotation and enters together with the stretched roving through the hollow spindle to a winding device, as disclosed, for example in, "eine neue Spinn-Zwirnmachine" published in "Melliand-Textilberichte", December 1966, pages 1354 and 1355.
In a method disclosed in German patent 44 28 780 a twisted yarn is produced in a first method step by removing two rovings from two roving supplies and guiding them through a stretching device. Thereafter, they are independently spun by a ring spinning process and then wound onto two bobbins permanently placed onto hollow spindles arranged on top of one another in order to produce to spun yarn bobbins. In a second process step, the spun yarns wound onto the spun yarn bobbins are then removed by forming a yarn balloon from the bobbins and guided through the hollow axles of the respective hollow spindles, while at the same time guiding the yarn of the upper hollow spindle also through the lower hollow spindle axle, and toward a winding device positioned below the lower hollow spindle. The hollow spindles are rotated as a function of the removal speed of the winding device such that the twist of the two spun yarns is partially cancelled.
In the two latter systems, ring spinning spindles are used whose yarns are subsequently guided to the twisting device.
It is an object of the present invention to provide a method for producing a twisted yarn with reduced curling tendency and reduced twisting moment (torque) which can be directly processed further without requiring ripening times or additional fixation methods as discussed above.